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Abstract

The asymmetric unit of the binuclear title compound, [Cd2(NCS)4(C24H20N6)2], contains one half-mol­ecule, consisting of one Cd2+ cation, two half 1,2-bis­{[2-(2-pyrid­yl)-1H-imidazol-1-yl]meth­yl}benzene (L) ligands and two SCN− anions. The dimeric cyclic mol­ecule is completed by crystallographic inversion symmetry. The Cd2+ cation is coordinated by two N atoms from two SCN− anions and four N atoms from two symmetry-related L ligands, exhibiting a distorted octrahedral coordination. A two-dimensional supra­molecular network stacked parallel to [210] is finally formed by linking these dimers through weak π–π stacking inter­actions between the pyridine rings and benzene rings of adjacent dimers, with a plane-to-plane distance of 3.36 (6) Å and a centroid–centroid distance of 3.67 (2) Å. One of the thio­cyanate S atoms is equally disordered over two positions.

supplementary crystallographic
information

Comment

Interest in cadmium compounds was provoked by their luminescent properties
(Yam & Lo, 1999; Zheng et al., 2004). A number of
cadmium compounds have
been reported with different N-donor ligands. In this paper, we present the
hydrothermal synthesis and crystal structure of the title compound, (I),
[Cd2(C24H20N6)2(SCN)4], based on the
1,2-bis{[2-(2-pyridyl)-1H-imidazol-1-yl]methyl}benzene ligand (hereafter
L).

The asymmetric unit of (I) contains one Cd2+ cation, two halfs of the
L
ligand and two SCN- anions. Two complete L ligands link two Cd2+
cations to form a centrosymmetric dimeric ring. So the asymmetric unit contains
only half of the
ring molecule (Fig. 1). The Cd2+ cation is coordinated to the N atom of two
SCN- anions and four N atoms from symmetry-related L ligands within
normal Cd—N distances (Dai et al., 2002; Luan et al.,
2006; Wang
et al., 2003). The resulting CdN6 polyhedron can be considered
as a
distorted octahedron. Each dimer links adjacent dimers viaπ–π interactions between pyridine rings and benzene rings to form
a 2D supramolecular network stacked along [210] (Fig. 2), with a plane to plane
distance of 3.36 (6) Å and a centroid-centroid distance of 3.67 (2) Å.

Experimental

A mixture of Cd(OAc)2.2H2O (0.13 g, 0.50 mmol), L (0.2 g, 0.5 mmol), KSCN (0.10 g, 1 mmol) and H2O (10 ml) was stirred for 1 h, and then
transferred and sealed in a 25 ml Teflon-lined stainless steel container.
The container was heated to 423 K, held at that temperature for 72 h, and
cooled to room temperature at a rate of 10 Kh-1. Colourless parallelepipeds
of (I) were collected in 78% yield.

Refinement

One of the SCN- groups is disordered over two positions. The S atom was
refined with a 0.5:0.5 occupancy ratio.
All H atoms on C atoms were positioned geometrically and refined as riding
atoms, with C—H = 0.93 Å for aromatic C atoms, and with C—H = 0.97 Å
for aliphatic C atoms, and Uiso=1.2 or 1.5Ueq(C).

Figures

A displacement ellipsoids view of (I), drawn at 30% probability level, showing two cations and one anion. All non-labelled atoms are generated by symmetry operator: 2-x, y, 1-z. H atoms were omitted for clarity. The two orientations of the disordered...

Special details

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes)
are estimated using the full covariance matrix. The cell esds are taken
into account individually in the estimation of esds in distances, angles
and torsion angles; correlations between esds in cell parameters are only
used when they are defined by crystal symmetry. An approximate (isotropic)
treatment of cell esds is used for estimating esds involving l.s. planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and
goodness of fit S are based on F2, conventional R-factors R are based
on F, with F set to zero for negative F2. The threshold expression of
F2 > 2sigma(F2) is used only for calculating R-factors(gt) etc. and is
not relevant to the choice of reflections for refinement. R-factors based
on F2 are statistically about twice as large as those based on F, and R-
factors based on ALL data will be even larger.